Musculoskeletal (MSK) disorders and particularly osteoarthritis (OA) are a major source of pain, functional impairment, and worsening quality of life across all age groups. Total knee replacement (TKR) is a costly, frequent intervention for knee OA. Its success is generally measured on the basis of implant longevity and pain relief. However, compelling evidence that moderate physical activity enhances overall health indicates that the value of TKR could be increased substantially if TKR recipients engaged in adequate levels of physical activity after rehabilitating from their surgeries. The evidence base in MSK and orthopedic clinical science has substantial gaps. I have devoted the last 15 years to addressing these research needs by designing rigorous patient-oriented research studies and mentoring younger clinical scientists. Through the next K24 cycle, I hope to continue to train young scientists in rigorous studies of MSK and orthopedic problems. In this competitive renewal application, I request five years of funding to enlarge and strengthen the mentoring and research programs. Aim I: To further strengthen my research training program, which focuses on preparing young investigators for rigorous patient-oriented research on MSK and orthopedic disorders. Aim II: To further develop a comprehensive patient-oriented research program in MSK and orthopedic disorders. I highlight two research studies in this proposal: Study 1: Portraying physical activity (PA) over 5 years among recipients of total knee replacement (TKR). Aim 1.1: To follow an established cohort of TKR recipients over 5 years to document long-term trajectories of engagement in PA. Aim 1.2: To determine risk factors for low or declining engagement in PA over 5 years post-TKR. Study 2: Raising awareness of knee OA and willingness to undertake behavioral changes to reduce the risk of knee OA. Aim 2.1. To develop an individualized web-based knee OA risk calculator that incorporates demographic and clinical factors to predict 5, 10, 15, 20, 25, 30-year and life time risk of symptomatic knee OA. Aim 2.2. To conduct a proof of concept randomized trial to establish whether the use of a knee OA risk calculator results in greater readiness for behavioral changes to reduce the risk of knee OA.